Notes from the workbench and beyond

Not Just Any Open Seam

Today I had a client in with a violin in need of gluing. While that in itself is nothing notable, there is an aspect of this encounter that may qualify as a teaching moment, especially apropos to those of us in the Northern Hemisphere who are heading into the heating season.

Violin family instruments are put together with hot hide glue, which has unique properties that are particularly advantageous in some circumstances. I’m not a “science guy” so I can’t answer questions about crystalline structure or tensile strength as opposed to other kinds of strength. I do know, for instance, that drywall screws have incredible holding power unless you whack’em sideways with a hammer, and for some reason, I am reminded of this when I think about violins and hide glue.

Hide glue, made from animal byproducts, is essentially the same friggin’ stuff that’s been used for hundreds of years in the assembly and repair of violin family instruments. The remarkable characteristics of this adhesive include its strength and its weakness. We have a wealth of instruments with top and back center joints that have retained their integrity for hundreds of years. Be thankful. Then we have the treble side upper bout and the lower bass side seams that, on so many instruments seem to open up on a regular basis. Again, be thankful.

Wood moves seasonally, especially here in New England. In moist weather, it swells. In dry weather it shrinks. Plain and simple. In my house here in Holyoke, the oak floors creak in the winter and in the summer, I can’t close the doors on the antique cherry corner cupboard without risking not being able to open them again until October. In my last house, the oak floors in my living room developed summer speed bumps that would have been the envy of any gated community.

An instrument seam glued with hide glue will break apart when stressed. This is a good thing in mid-winter when the heat’s been on and the wood shrinks. It’s preferable to having the wood itself crack. Having open seams glued is a normal part of violin/viola/cello maintenance. This characteristic of hide glue is also the reason that it is even possible to disassemble an instrument to do interior repairs. So we’re thankful, right?

That said, if a violin maker/restorer is smart, and skillful, he or she will take advantage of the properties of the materials at hand, in this case I’m considering the glue. Hot hide glue can be mixed in ways that varies its strength. A fresh pot of glue will be strongest. With repeated heatings, its strength diminishes. The strength can also be altered depending on the proportion of water used in the batch. Theoretically, one would be very smart to use the strongest glue, say, for the center joints in the top and back, for setting the neck joint, and for joining fresh cracks. It may be smart to use a weaker glue mix for securing the fingerboard, and assembling the top, which could be subject to seasonal stresses. Remember, an open seam is preferable to a crack.

Speaking as a restorer, we like the fact that hide glue is reversible. It may seem counter intuitive, but the reversibility of hide glue actually increases the chance that an instrument will live a very long life.

Back to my client, who was smart to call in an emergency. She was concerned with the lower block area of her violin, which looked like this (violin is viewed with the back up, so we can see the area where the tailpiece is anchored by the end button):

Indeed, the glued seam had released, but in this case, the loose seam extended over the lower block, leaving the body of the instrument vulnerable to the longitudinal string tension. I suspect that the end grain of the lower block was improperly sized on this relatively “new” instrument, before the top was glued on, causing the area to seperate.

One can see from the photo how the string tension has compressed the body from end to end, and the button/rib assembly has abandoned the original glue line. The lower block is no longer secured to the top, and the spruce top is now bearing more than its share of structural tension. Not a good scenario, structurally speaking, BUT one that is easily remedied at this stage. When I loosened the string tension, my client and I both heard the lower rib/block area pop back into place.

This story ends with a simple gluing and a happy violinist! The moral of the story is that all open seams are not created equal. This particular seam opening demanded immediate attention due to the structural issues it presented.

4 Responses

In Australia, we experience very hot summers. Is it more likely for my violin to experience seam bursts? My instrument is just over six years old and was made in Czech republic. Any rate, I will regularly check it.

Another interest question, but have you seen many cases where a shoulder rest causes damage to the instrument?

I wouldn’t presume to know anything about Australia, although I can say that I know a couple of Australians that I like very much!

I started responding to your comment about hot summers/extremes in temperature and realized I was writing so much that perhaps another post is in order. So stay tuned for that. I hope to have that up within a couple of days.

About the shoulder rest question: shoulder rests and chinrests are about player comfort. When you are comfortable, you will play your best, and your overall experience will be maximized.

I have seen damage done by shoulder rests and chin rests. Usually, in the case of a shoulder rest, this means that the varnish is worn or chipped away where contact is made on the edges or the ribs. A shoulder rest should be adjusted so that it fits securely without exerting undue pressure on the instrument (same with a chin rest). The shoulder rest should not touch the middle of the lower back. It also should have healthy padding on its “feet” so that abrasion is minimized as you take it on and off.

A shoulder rest that fits properly should not inspire seam openings, if that’s what you are getting at. It is possible that a shoulder rest can influence the tone slightly but chances are that your comfort will influence it even more!

Can you expand on the “end grain of the lower block was improperly sized”? Did you glue top to rib only or also get glue atop the block?

Week after next will be my second top-off violin attempt. I’ve done a cello jigsaw puzzle top and only ended up with a few extra pieces. Aside from room to work or clamp storage issues, have you heard anyone say it is easier to learn on larger instruments?

Hi Jim –
Because end grain is so porous, it absorbs more glue. If the blocks (end blocks or corner blocks) are improperly sized, too much glue is absorbed into the block upon assembly, resulting in a weakened seam. The lower block, in particular carries a lot of load due to the string tension. Sizing simply means to coat the end grain with hot glue, allow it to dry, and re-level if necessary, before the final assembly.

About working with hide glue – it is possible to vary the strength of the mix, and while you want good adhesion, you also don’t want to over glue. Instruments should be glued so that they can be taken apart again!

My advice to learners is to find instruments with a value commensurate with their skill level, ie keep the risk low until you develop a competent skill set. Keep in mind that it is always harder (and more expensive) to redo a bad repair than to do a repair well the first time. So choose your projects wisely.

Larger instruments are more to handle, and their problems can be compounded by their size. I don’t think they are in any way easier to work on. I will always recommend working on smaller instruments first.

Lastly, I highly recommend taking a workshop or seminar in repair. There are several on offer. The absolute best way to further your skills is to have some mentoring or tutoring. A class setting allows you to meet like minds and see lots of instruments.